In its most basic implementation, the auth0.login Snippet redirects the User to your Auth0 domain's login page, then calls the Auth0 API to identify the User by their verified email address. If a MODX User record exists with that email, the auth0.login Snippet attempts to verify the User against the MODX User records, and if successful, adds the MODX Context(s) specified in the Snippet properties, to the User's session.